JP2790850B2 - Cellulose thin film for pellicle - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photomask in a photolithography technique, and a pellicle thin film used for protecting a reticle.

(Prior Art) A pellicle made of a thin and transparent film is used for protecting a photomask and a reticle, and is useful for improving productivity in photolithography during a manufacturing process of a semiconductor device. A commonly used pellicle is fixed to a photolithography mask, and is located on the mask at a predetermined distance from the mask. Therefore, during the photolithography operation, fine dust particles do not form an image on the work surface even if they adhere to the pellicle. Therefore, by protecting the mask or reticle with the pellicle, it is possible to prevent the dust particles from adversely affecting the silicon wafer, improve the production yield of the integrated circuit chip, reduce the number of times of cleaning of the mask, and shorten the life of the mask. There are effects such as stretching.

Currently, commercially available pellicles have 0.8μ
It is a thin film made of nitrocellulose having a thickness of m to 7 μm. A pellicle made of such a nitrocellulose thin film is satisfactorily satisfied with the current g-line (436 mm) photolithography technology.

(Problems to be Solved by the Invention) With the recent progress in the semiconductor industry, there is a tendency for integrated circuits to have higher densities and higher integration, and both the line width and the line interval of the projected pattern on the wafer have become smaller. I have. Therefore, as an exposure light source, h-line (406 mm) and i-line (365 mm), which have shorter wavelength and higher energy than g-line (436 mm)
Has come to be used.

The pellicle composed of a nitrocellulose thin film has good light resistance at g-line and is satisfactory for the time being.
Nitrocellulose degrades when it comes to high energy h-line or i-line, and cannot be used. Therefore, cellulose derivatives are currently being studied as a material to replace nitrocellulose. As cellulose derivatives,
There are cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, etc., and these materials have better light resistance than nitrocellulose, but the disadvantage of a thin film made of it is that when it is placed in a high humidity environment, it will sag. It is difficult to keep in tension because wrinkles occur. An object of the present invention is to provide a pellicle thin film which has good light fastness even in h-line and i-line and does not generate slack or wrinkles even in a high humidity environment.

(Means for Solving the Problems) The present invention relates to a nitrocellulose of 10 to 50 wt% and at least one of cellulose acetate, cellulose acetate butyrate and cellulose acetate propionate of 90 to 50%.
a pellicle thin film comprising a composition consisting of wt%.

The pellicle thin film of the present invention has no sagging or wrinkles even in a high-humidity environment, and has much better light resistance to h-line and i-line than a thin film composed of only nitrocellulose.

The present invention will be described in more detail. The pellicle thin film made of nitrocellulose does not degrade at g-line (436 mm) light and has good light transmittance, but degrades remarkably at light having a short wavelength of 365 mm or less. In recent semiconductor photolithography techniques, there is a tendency for integrated circuits to have high density and high integration, and both the line width and line interval of a projection pattern on a wafer have become smaller. For that reason,
Shorter wavelength light has come to be used as an exposure light source. Therefore, each pellicle maker has devised a pellicle using various cellulose derivatives as a pellicle material having good light transmittance even at a short wavelength and having light resistance. As a cellulose derivative having light resistance at short wavelengths, a pellicle made of cellulose acetate, cellulose acetate butyrate, or cellulose acetate propionate has been devised, but a pellicle using a thin film made of these cellulose derivatives has been proposed.
In any case, the shape retention is poor at high humidity. That is, sagging and wrinkling occur in the thin film at high humidity. In the process of photolithography of semiconductors, fine dust due to static electricity, to avoid adherence to equipment, products, etc., tends to maintain a relatively high relative humidity in the room, such a thin film, Not practical.

The pellicle made of the thin film of the present invention is a pellicle which is free from sagging and wrinkles even in such a high-humidity environment, has good light resistance at low wavelengths of h-line and i-line, and can withstand practical use. .

Nitrocellulose to be mixed with cellulose derivatives other than nitrocellulose such as cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate is preferred because the higher the molecular weight, the greater the shape retention of the thin film, and the degree of nitrification is preferably 10%. 1313%, preferably 11-12%. Such a material is commercially available from Asahi Kasei Kogyo Co., Ltd. and has a nitrification degree of 10.7-12.2.
%. This commercial product contains various paints, inks, adhesives,
It is widely used for many applications such as coating materials.

As a cellulose derivative other than nitrocellulose used by mixing with such nitrocellulose, it can be mixed with nitrocellulose to form a film of 0.5 to 15 μm, preferably 0.8 to 10 μm, and the obtained film absorbs light of 365 mm. Any cellulose derivative can be used as long as the scattering is 5% or less, preferably 2% or less.

Those satisfying such conditions are cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate.

Among these cellulose derivatives, those having a degree of acetylation of 20 to 55%, preferably 40 to 55%, are preferably used as cellulose acetate. Commercially available products from Eastman Kodak Company can be used, which have a degree of acetylation of around 55%.

Also, as cellulose acetate propionate,
Those having a propionyl content of 10-46%, preferably 40-46%, can be used.

Among these cellulose derivatives, cellulose acetate butyrate has particularly high utility, and it is preferable that the cellulose derivative has a higher butyryl content and a higher molecular weight. One example of a preferred composition of cellulose acetate butyrate has a butyryl content of 40-55 wt%, preferably 50-55 wt%.
~ 55wt%, number average molecular weight 40,000 ~ 100,000
Good. This material is commercially available from Eastman Kodak Company and can easily be obtained with a number average molecular weight of 40,000 to 70,000.

In the present invention, a mixture of cellulose acetate butyrate and nitrocellulose is most preferred. In the present invention, the mixing ratio of nitrocellulose is 10 to 50% by weight.
Is good. When the mixing ratio of nitrocellulose is less than 10 wt%, there is almost no effect on the thin film shape retention in a high humidity environment, and when the mixing ratio of nitrocellulose exceeds 50 wt%, the thin film shape retention is extremely effective. Although light resistance at h-line and i-line is slightly better than nitrocellulose, it deteriorates in a short time.

Considering the long-term thin film shape retention and light resistance at h-line and i-line, the mixing ratio of nitrocellulose is
20-40 wt% is preferred.

Since nitrocellulose is the same cellulosic system as cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, etc., the compatibility is very good.

The pellicle is used by being installed in an optical path between a light source of an exposure apparatus and an optical lens system. Therefore, the thin film of the pellicle must have uniform light transmittance in the plane of the film, and at the same time, does not substantially affect the deviation of the path of the exposure line that may be caused by the refractive index of the thin film. Must be of uniform thickness. Further, the film is required to transmit an image without distortion and without disturbance, and it is required that the film has uniform thickness, no dust and scratches, and no internal distortion.

The film thickness of the pellicle thin film of the present invention comprising a mixed composition of nitrocellulose and cellulose acetate, cellulose acetate butyrate, and at least one of cellulose acetate propionate is in the range of 0.5 to 15 μm, preferably 0.8 to 10 μm. . If the film thickness is made thinner than this, the mechanical strength is reduced, and sufficient care must be taken in handling such a pellicle. If the film thickness is larger than this, the light transmittance tends to decrease due to minute roughness of the film surface.

The thin film of the present invention may be produced by any method. However, since nitrocellulose is not thermoplastic, a method of casting in a solution is usually used. Further, in the pellicle of the present purpose, the film thickness is 0.5 μm to 15 μm
The spin coating method (spin coater method), knife coater method, dip-pulling method, casting method on the fluid surface, etc. are suitable for the production method because thinness is important and uniformity of the film thickness is important. However, the spin coater method is particularly preferable.

Such a thin film of uniform thickness, nitrocellulose and cellulose acetate, cellulose acetate butyrate,
At least one of cellulose acetate propionate and a predetermined mixing ratio, and so as to have a concentration, dissolved in a solvent such as ethyl lactate and cyclohexanone, and filtered,
It can be made by casting on a smooth substrate such as a glass substrate by a spin coater method or the like.

However, the spin coating conditions for obtaining the thin film of the present invention involve many influential factors such as the fluidity of the solution, the volatility of the solvent of the solution, the temperature around the spin coater, the humidity, the spin speed, and the spin time. Choose the right to achieve the goal.

The thin film formed on the glass substrate or the like is peeled off from the substrate, stretched over a metal frame or the like, and fixed with an epoxy-based adhesive or the like.

The thin film in the pellicle shape manufactured in this manner has a good thin film shape retention property even in a high humidity environment, and has no sagging or wrinkles, as well as short-wavelength light h-line or i-line. Has sufficient light transmittance and is sufficiently practical.

As described above, the present invention, by mixing nitrocellulose and cellulose acetate, cellulose acetate butyrate, at least one of cellulose acetate propionate, in high humidity, sagging and preventing the occurrence of wrinkles, at a short wavelength The present invention relates to a pellicle thin film characterized in that light resistance is also improved. Further, for example, it is also possible to prevent reflection by a polymer coating as described in JP-B-63-22576.

(Example) Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

Example 1 8.0 g of cellulose acetate butyrate (abbreviated as CAB; 531-1 manufactured by Eastman Kodak Co., butyryl content, 50%)
And nitrocellulose (abbreviated as NC; H-100 manufactured by Asahi Kasei Corporation)
2.0 g (degree of nitrification: 12.0%) was dissolved in ethyl acetate cellosolve to prepare a solution having a solid content of 5.0 wt%. Set the silicon wafer on the spin coater (rotary coating machine)
20 cc of the prepared CAB / NC solution was dropped, and then the silicon wafer was rotated at 900 rpm for 30 seconds. Then, the thin film was peeled off from the silicon wafer, stretched tightly on a rectangular aluminum frame of 120 × 98 mm, and fixed with an epoxy adhesive.
The thin film was left in a watered desiccator at a humidity of 100%, and showed no sagging or wrinkling. No abnormality was found even after one month.

Example 2 Cellulose acetate (abbreviated as CA; manufactured by Daicel, L-40)
F, acetylation degree 55%), 5g and nitrocellulose (Asahi Kasei Kogyo,
H-1000, nitrification degree 12.0%) was dissolved in ethyl lactate to prepare a solution having a solid content of 2 wt%. In the same manner as in Example 1, a thin film having a thickness of 1.0 μm was formed using a spin coater.
It was firmly attached to a rectangular aluminum frame of × 98 mm with an epoxy adhesive. 100% humidity with water on this thin film
It was left in the desiccator, but no sagging or wrinkling occurred. Also, after one month,
No anomalies were seen.

Example 3 Cellulose acetate propionate (abbreviated as CAP)
7.0 g of Eastman Kodak Co., Ltd., 482-20, propionyl content, 46%) and nitrocellulose (H-1 manufactured by Asahi Kasei Corporation)
3.0 g was dissolved in ethyl lactate to prepare a solution having a solid content of 5 wt%, and the same spin coater method as in Example 1 was used to form a thin film having a thickness of 1.7 μm. It was firmly attached to a rectangular aluminum frame with an epoxy adhesive. This thin film was left in a desiccator at a humidity of 100% with water, and no sagging or wrinkling occurred. For reference, the spectral characteristics of this thin film are shown in FIG.

Example 4 Each solution was prepared for cellulose acetate butyrate (381-20, manufactured by Eastman Kodak Company, butyryl content, 37%) and nitrocellulose (H-120, manufactured by Asahi Kasei Kogyo Co., Ltd.) at the following ratios, and the same as in Example 1. In the method, a thin film of each composition was prepared, fixed to an aluminum frame, and left in a desiccator of 100% humidity with water. CAB 100% thin film wrinkled, nitrocellulose 10 wt% thin film slightly wrinkled, The CAB thin film containing nitrocellulose of 20 wt% or more did not have any sagging or wrinkling.

Example 5 7.0 g of cellulose acetate butyrate (531-1, manufactured by Eastman Kodak Company, butyryl content, 50%) and 5 g of nitrocellulose (H-500, manufactured by Asahi Kasei Kogyo, nitrification degree 12.0%) were dissolved in ethyl acetate cellosolve. Then, a solution having a solid content concentration of 6.0 wt% was prepared. A fluorinated methacrylate resin (refractive index, n = 1365) was dissolved in perfluorotributylamine to prepare a 0.8 wt% solution.

Set the silicon wafer on the spin coater, CA
By dropping 20 cc of the mixed solution of B / NC and rotating at 900 rpm for 30 seconds, a thin film of CAB / NC was formed on the silicon wafer, and the solvent was evaporated using a hot plate. Next, 3 cc of the fluorine-containing methacrylate solution was dropped on this, rotated at 600 rpm for 30 seconds, and dried. And
A thin film having a two-layer structure was formed.

On the other hand, on the end face of aluminum frame (outer diameter 120 × 98mm)
An epoxy adhesive was applied, and this was superimposed on the fluorine-containing methacrylate layer side of the thin film, and the epoxy was cured to bond the frame and the film. This is immersed in water, left for 30 minutes to separate the wafer and the film, the frame with the film is taken out of the water, air-dried, and set again on a spin coater so that the film surface faces up. By forming an acrylate coating film, a 3.1 μm-thick non-reflective pellicle having a target multilayer film having a three-layer structure was obtained.

The spectral characteristics of this pellicle are 365 mm as shown in FIG.
Light transmittance is 95% ~ 99.5% and the average transmittance is 9
It was as high as 7.25%. Humidity when this film is watered
When placed in a 100% dessicator, there was no sagging or wrinkling.

Comparative Example A thin film was formed from each of cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and nitrocellulose used in Examples 1, 2, and 3, and their moisture resistance and light resistance were compared.
The moisture resistance was determined by the thin film retention property (the occurrence of sagging and wrinkling) in a humidity of 100%, and the light resistance was compared by the time until transfer by i-ray (365 mm) irradiation occurred. The transfer is a phenomenon in which a difference occurs in the color of a thin film between a portion irradiated with light and a portion not irradiated with light. That is, optical distance = film thickness × refractive index. Table 1 shows the comparison results. Measurement of transcription, a half of the film covered with aluminum foil, Wacom Co., a UV solar simulator, 365 mm, irradiated with light of 50 mw / cm ^2, the color of a thin film of non-irradiated portion covered by the irradiation portion and the aluminum foil The time until the difference appeared was defined as the time until transfer occurred.

As can be seen from this comparative example, the thin film of the present invention has good shape retention at high humidity, and has a longer time to transfer, compared to nitrocellulose alone, and has excellent durability. It turns out that there is.

(Effects of the Invention) As described above, according to the present invention, a uniform and defect-free thin film can be easily produced, and the thin film has extremely high transparency and durability in a wide wavelength range from near ultraviolet to far ultraviolet. It is good and has no sagging or wrinkles even in a high humidity environment, and its performance is stably maintained, which is useful for improving the productivity of semiconductor integrated circuits.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the wavelength (nm) and the light transmittance (%) of the thin film composed of cellulose acetate propionate and nitrocellulose produced in Example 3, and FIG. 4 is a graph showing the relationship between the wavelength (nm) and the light transmittance (%) of a manufactured thin film having a three-layer structure in which an antireflection coating is applied to a thin film made of cellulose acetate butyrate and nitrocellulose.

Claims (1)

(57) [Claims] 1. A nitrocellulose of 10 to 50% by weight and at least one of cellulose acetate, cellulose acetate butyrate and cellulose acetate propionate.
A thin film for a pellicle comprising a composition consisting of wt%.